Resonant combustion products generator with heat exchanger



May 24, 1960 A. G. BODINE, JR 2,937,500

RESONANT COMBUSTION PRODUCTS GENERATOR WITH HEAT EXCHANGER Filed Oct. 2.1957 3/ f|||\ 32 33 F1G..1.

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I- 5 I I I United States Patent RESONANT COMBUSTION PRODUCTS GENER- ATORWITH HEAT EXCHANGER Albert G. Bodine, Jr., 13120 Moorpark St.,

Van Nuys, Calif.

Continuation of application Ser. No. 229,573, June 2, 1951. Thisapplication Oct. 2,;1957, Ser. No. 687,67 1

2 Claims. (Cl. v 60 -3957) This invention relates generally to resonantjet engines in combination with heat exchange equipment, and isespecially concerned with the provision, in connection with a resonantjet engine, of a heat exchangen'for use either in heating the air supplyto the engine, or fluid to be utilized for a separate purpose,which-heat exchanger is characterized by a sonically augmented rate ofheat transfer. This application is a continuation of my applicationSerial No. 229,573, filed June 2, 1951, entitled Resonant Jet Enginewith HeatExc hanger (now abancloned) and a continuation-in-part of myprior applications entitled, Method and Apparatus for Generating aControlled Thrust, filed April 21, 1942, "Serial Np,-439,926

' (now abandoned), and Method and ,Apparatus for-Boundary Layer Control,filed September 2,;1947, Serial No. 771,808 (now abandoned).

An object of the invention is the provisionofa resonant jet heat engineand heat exchanger ofimproved rate and eflicacy of heat transfer.

A further object is the provision of a resonant jet heat engine having anovel and improvedarrangement of heat exchanger for preheating the airutilized for combustion.

The invention utilizes acoustic wave action to break down and scrub awaysluggish, heat insulating boundary layers of gas which cling tenaciouslyto the heat receiving be understood that an acoustic wave, comprisesalternating waves of elastic compression-and rarefaction in an elasticmedium. In accordance with the'invention, the-sub-laminar layers ofstagnant gases which cling to the'heat-exchange walls become a reactancein theacoustic wave circuit, and because of the high velocity activityof the standing Wave in the region of the velocity antinode, thesesub-laminar layers of insulating gases are exposed or subjected. tovigorous sonic frequency. agitation, and there- .by, disrupted andscrubbed .fromthe wall surfaces. The

effect is maximized: at the velocity anti-node region, where 'thevelocity and kinetic energy of particle oscillation is at a maximum. Theactual breaking away of the boundary layer is thus owing to its becominga reactance in the acoustic circuit in which the wave is created,whereby it becomes exposed to acoustic wave agitation. This dissipationof the boundary layer results in asharp increase in heat transmissioncharacteristics.

The invention will be understood bestbyreferriugnow to certainillustrative embodiments, thereof, reference ,for

2,931,500 Patented May 24 1960 ice 2 this purpose being had to theaccompanying drawings, in which:

Figure 1 is a longitudinal sectional view of a resonant jet engine andheat exchanger in accordance with the invention; a

Figure 2 is a similar view of a modified form of the invention; and vFigure 3 is a similar view of another modified formof the invention. p

In Figure 1, numeral designates an acoustic resonant cavity, here in theform of a metallic sonic pipe having a closedhead end 11 and an open end12 through which products of combustion are discharged to atmosphere. .Acombustible mixture is introduced into the zone P of pipe 10 through anintake valve 13, which maybe of the spring-loaded type, so that it openswhenever the pressure in a fuel induction passage 14 exceeds thepressure in zone P by a predetermined amount. A supercharger 15, drivenby means not shown, supplies the airfuel mixture to the .fuel inductionpassage 14. A car buretor 16 forms and delivers the fuel-air mixture tothe intake of the supercharger. H I

16 passes first through a preheater in the form of a heat exchanger 20,comprising a jacket around pipe 10 and to which air is supplied througha mouth 21, thus obtaining a heat exchange between the incoming air andthe heated column of combustion gases contained inside pip e lll duringtheoperation of the engine. I

The charge of fuel introduced to the combustion zone.

at P by way of passage 14 and valve 13 is ignitedas by means of sparkplug 22, and the resulting explosion produces a sharp pressure rise atZone P, causing a wave of compression to be launched down the column ofgas contained in pipe 10, this compression wave traveling with the speedof sound in the heated combustion gases.

This compression wave will be refiectedfrom the open end 12 of the pipe10 as a wave of rarefaction, which upon reaching the zone P will producea pressure depression, causing valve 13 to open,- and an additionalcharge of fuel mixture to be introduced to zone P. The described wave ofrarefaction is reflected .by ,the closed end of pipe 10 as a wave ofrarefaction traveling back I towards the open end of the pipe, and this.latter wave is in turn reflected by the ,openend of the pipe asa waveof compression returning toward the. head end of the pipe. If thearrivalof this wave of compression coincides with the next ignition offuel-air mixture and resulting pressure increase at zone P, are-enforced pressure peak occurs at P, with increased fuel density andincreased compression ratio, thereby very' materially improving thecombustion cycle. Also, tofollowon with the succeeding cycle, are-enforced or augmented wave of compression is started down the pipe 10from combustion ZoneIP, and

the-cycle as previously described is then repeated, .but with thepressure cycle traveling through meater amplitude swing as compared withthe initial cycle. Under these conditions, a condition of quarter-waveresonance is established, with a pressure anti-node (zone of maximumpressure variation) at P, and a velocity anti-node V (zone of'rnaximumvelocity variation) at the far, open end,12 of the pipe, which functionsas a guide for a standing wave in the combustion. gases. While it isfound'in practice that the returning wave of compression so increasesthe pressure and density of the fuel-air mixture at. the zone P as tocause ignition even without the' continued use of spark plug 22,apparently by 'reason of an attenuated after-flame remaining in the zonePthroughout the reduced pressure part of the cycle, the embodiment ofFigure 1 includes an automatic timing system .f or energizationoffhespark plug 22. As showm the The air entering carburetor qu'arter-waveresonance, with a pressure anti-node at P, 'and'a velocity anti-node Vat theopen end of the pipe. In other words, a; quarter-wave lengthstanding wave is :established in the gas column in the pipe. ,Ihisstanding "wave results inscrubbing the hot combustion gases against,fthe inner surface of pipe 10, inhibiting any tendencytowardaccumulation of heat-insulating boundary layers of stagnant gasesadjacent the inside surfaces of the pipe. fflhe velocityaction of thestanding wave at the velocity antinode region, and the pressurefluctuation action at the pressure antinode region, gradually merginginto 'onefanother'along the pipe 10, both have a dispersive action "onthe gaseous boundary layer tending to cling to the insidesurfaces of thepipe. .Theboundary layer gases 'of acoustic wave system, and experiencedisruptive acous- \30 tic forces owing thereto. The standing wave actionin the "column of gases also induces soundwave transmission pressurecycle and a standing wave as described-in con-' of which includesbattery 31 and amake-break switch 32,

the latter beingactuated by a plunger '33 connected to a diaphragm 34urged in a direction to close the make and "break switchby a spring 35.One side of the diaphragm :isconnected through passage 3 6 with the gascolumn in "pipe at zone P. Upon the appearance of each positive pressurepeak or pulse 'at P, diaphragm 34 moves upwardly'to break the lowvoltage circuit, causing the. high "tension coil to produce a spark atplug 22. This spark thus be, synchronized with the appearance ofpositive pressure pulses at zone P.

As explained, the operation of the system produces actually become areactance in a distributed constant type within .or through the wallsofpipe which'form the guide for the standing Wave, producing a waveaction at theoutside surface of the pipe which is in turn transmitted tothe fluid'inside jacket.-20. Stagnant boundary layer'conditions adjacentthe external's urfaces of pipe 10 within jacket are thereby reduced oreliminated, en-

abling intimate contact of the unheated air with the ex- "terior ofheated pipe 110, and hence increasing the heat fjexchange rate, andtherefore the heat input to the airfuel mixture to be introduced intopipe 10 for combustion.

By. this means I'believe I have accomplished more efiective pre-heatingof intake air for engine combustionthan has heretofore been known.Flgure 2 shows an embodiment of the invention accord ing to which theheated'fluidis to be used, not for a supply to the. engine, but'for someseparate purpose. The

- i engine in thisinstance is similar in all essential respects I tothat OfFig'ure 1,. including pipe 10a having a closed head end 11a andopen end 12a for discharge of products of combustion. The combustiblemixture is introduced new? the high voltage terminal thereon. The rateof heat transfer is thereby very ma- 1 terially improved. The embodimentof Figure 2 accordingly comprises a resonant jet engine employed as aheat I source for a body of fluid to be heated by heat exchange,

r 4 case, the'sparkplug is energized once, for starting purposes,through any suitable electrical energizing device,

not shown, and combustion then occurs on each pressure peak at zone P asa result of the high compression and increased fuel density, whichcauses the fuel to ignite by reason of a residual or lingering flamealways present at the zone P, but too attenuatedexcepting at thepressure 7 peak phases'of the cycle to ignite the fuel mixture.

..,Heat transfer from the heated combustion gases inside pipe 104 to thefluid passingthrough heat exchanger 20a proceeds in the manner describedin connection with Figure l, the sound wave action prevalent inside thepipe 10a-acting to scrub the hot combustion gases against the f inside"of the pipe and thereby prevent boundary layer accumulation thereon,and acting also through the walls of the pipe to prevent boundary layerconditions in the fluid surrounding the pipe inside the heat exchanger.The wave system is of the distributed constantstype, and the boundarylayer becomes a reactance in the acoustic circuit, with resultingcontinuous acoustic disruptive action the standing wave maintained.inside the engine removing boundary layer conditions adjacent the enginewall through which the heat is to be'transferred and thereby appreciablyincreasing the heat transfer rate.

';Figure 3 shows another modification, designed particu-. larly forairheati ng, where the heated air is to be'used 1 for a purpose otherthan as a supply to the engine. Numeral 50 designates generally aU-shaped sonic pipe,

I having legs 51 and 52,, formed at their ends with enlarged sections 53and. 54, respectively, to provide combustion chambers. The two legs 51and 52 are connected by semi-circular pipe section 55, and the latterhas, opening from the midpoint of its convex side, a fluid discharge vpipe 56. The U-tube as thus described is surrounded by heat-"exchang'e'r60, which ,comprises'a jacket having an endwall 61 through which openthe enlarged end 'portions 53 and 54 of the U-tube, and with end wall 62i joined to discharge'pipe '56 just beyond pipe section 55, clearlyshown. The jacket also has 'air inlet 63, and

. outlet 64. Anair and fuel induction system 65 is here shown in theform of a U-tube 66 having legs 67 and 68 formed with enlarged endportions 69 and 70, respecinto zone'P of pipe 10a through spring-loadedintake valve 13a, whichyalve opens whenever thepressurelin fuelinduction passage 14a exceeds the pressure at P by a predeterminedamount. Supercharger 15a supplies the air-fuel' mixture to fuelinduction passage 14a. Carbu "retor 16a delivers .the air-fuel mixtureto the intake of the supercharger, and is shown in Figure 2 as takingits t air from'atmosphere, although it would be within the scope of'theinvention to have the carburetor receive a portion of the air preheatedby the heat exchanger :presently to be described.

Heat exchanger20a, comprising a jacket around 'pipe 10a to which 'air issupplied through mouth 21a, has a heated fluid delivery pipe 40a leadingto some means for utilizing the same, not shown. The fuel chargeintroduced to the combustion zone at P is ignited as by means of sparkplug 22a, and theresulting explosion produces a nection with theembodiment of Figure 1. No automatically timed means is shown for theenergization of the spark plug in the instance of Figure 2, since asdescnbed earlier, the apparatus is actually found to operate, L I oncestarted, without use -of electric ignition. Inthis' "*thusoccurat P andP, each sending a pressure wave.

tively, bolted or otherwise fastened to heat exchange end induction pipe73 discharges inside U-tube 66at the mid- 3 point thereof and preferablyon its concave side, as shown. A spark plug 74,-used onlyfor starting,is mounted in the enlarged induction pipe portion 69.

T In operation, fuel introduced through pipe 72 and air introducedthrough pipe 73 travel around the two legs '67 and 68 of U-tube 66 tothe two combustion zones,

which coincide with pressure anti-nodes P and P of a sonic standingwaveset up as presently to be described. The air' may be introducedthrough pipe 73 either by means of a blower, not shown, or by suctiondeveloped in a mannerto be described hereinafter. The fuelmix turereaching the, zone P is ignited by means of spark plug 74 and theresulting explosion sends a positive pressure' wave'pulse in the columnof gases extending around the U -tub e 50 to the. othercombustion zoneat -P. As

7 the resulting pressure peak builds up' at, P, the fuel v thereat,sending a positive pressue wave pulse around the density increasessufficientlythat anrexplosion occurs U-tube 50 in a reversedirectionhThis last mentioned pressure wave, upon reaching the zone P, produces afur- 1 'therjexpl'osion at P, and so on. Alternate explosions ahalf-wave sonic .pipe.. Also, acoustic standing wave i s setup in the"column of "gases 'insaid pipe, the zones 1.

-P' being-pressure-anti anti-ridde-V appears at the juuctute or the twolegs 51 de' zone's, and alvelocity and 52, opposite the discharge pipe56. At the zone V, the combustion gases oscillate back and forth, asvindicated by the double-headed arrow. A standing sound wave is thusestablished in the U-tube, with maximum pressure variation oznes at Pand P, and with a maximum velocity variation zone at V, the hotcombustion gases first rushing in one direction around the curvedportion of the U-tube, and then in the opposite direction, in analternating or oscillating type of flow. The system is of thedistributed constants type, and the boundary layer becomes a reactancein the acoustic circuit, with resulting continuous disruptive actionthereon.

'In addition to the oscillating motion of the gas in the region V owingto the standing sound wave, there is a relatively slower continuous flowof combustion gases down the two legs '51 and 52 and. out the dischargepipe 56. This discharge of combustion gases from pipe 56 is promoted bycentrifugal forces acting on the combustion gases in the curved section55 of the U-tube. The gas velocity is very high, and substantialcentrifugal forces are set up in the combustion gases traveling aroundthe curved section 55, causing them to be crowded radially outwardtoward the outer peripheral wall, and thereby setting.

up a substantial pressure differential in a radial direction across thepipe section 55 opposite or in line with the discharge pipe 56. Thusthere is an elevated pressure at tslke outer wall, aiding fluiddischarge through the pipe In the embodiment of Figure 3, the air andfuel inductlon U-tube 66 is given a length equalto a half-wave lengthfor the resonant frequency of the pipe 50, and a standing wave' occursalso in the pipe 56, with a velocity anti-node V' at the midpoint. TheU-tube 66 is considerably shorter than the U-tube 50, because of thedifference in temperature of the gases in the two U-tubes, the highlyheated gases in the U-tube 50 resulting in an increase in the velocityof sound, and a corresponding increase in wave length for a given wavefrequency. Thus, the distances from the point of air intake into U-tube66 to the two combustion chambers at P and P are equal to quarter wavelengths for the sound wave set up in the system, and under theseconditions, as set forth in my Patent No. 2,731,795, the two legs 67 and68 feeding fuel mixture to the two combustion zones are intake pipes ofhigh acoustic impedance capable of opening directly into the combustionchambers without use of valves, and without loss of sonic wave energyfrom the U-tube 50 back into the induction system. Owing to the velocityanti-node condition established at V, in line with air intake pipe 73,the air and fuel mixture within the U-tube 66 oscillates at the sonicfrequency of the system around the curved section of the U-tube 66, andcentrifugal forces are set up in a radial direction across the inductionpipe creating a pressure depression at the concave side thereof, whichaids in sucking air into the system through the pipe 73.

The acoustic wave action along the column of gases, and in particularthe vigorous, sonic frequency gas oscillations in the velocity anti-noderegion of U-tube 50, scrubs away stagnant boundary layer gases, and thusincrease the heat exchange rate. An important advantage of the system ofFigure 3 over the earlier decribed em,- bodiments from a heat exchangestandpoint is that the heat exchange jacket encloses the entirety of thesonic pipe 50, including particularly the entirety of the velocityanti-node portion of the pipe. In the earlier described embodiments, acertain length of the sonic pipe adjacent the discharge outlet operatesat a relatively low temperature,:resulting from the alternating 'gasflowinto and'then back out of the tail of the pipe at velocity anti-noderegion V. Outside air is thus alternately sucked into and dischargedfrom the tail portion of the pipe in the embodiments of Figures -1 and2, andhas a-definite cooling .eifect,.so that theheat exchanger :shouldnotenclose :the jitail portion of the pipe, but shouldterminatesubstantially short thereof, and considerable heat is lost. There is nosuch action with the system of Figure 3, the velocity antinode region Vbeing confined within the U-tube, and the discharge from exhaust pipe 56being entirely unidirectional. Thus it will be seen that the heatexchange jacket,

in the case of the embodiment of Figure 3, can be arof the engines mayobviously be installed inside a single heat exchanger jacket.

The invention has now been embodied in certain present illustrativeforms of apparatus, but it will be understood that these are merely forillustrative purposes only, and that many changes in design, structureand arrangement may be made without departing from thespirit and scopeof the appended claims.

I claim:

1. A heat generating plant comprising, in combination, a pulse engine ofthe type embodying an acoustic cavity having walls defining a conduitfor a combustion gas column, said conduit having air intake and gasdischarge ports, and said walls also defining a guide for an acousticstanding wave having pressure and velocity antinode regions spaced alongsaid conduit, said cavity having a combustion chamber at a pressureantinode region of said standing wave, combustion control means inconjunction with said chamber for exciting said standing wave at anacoustic resonant frequency of said cavity, and a heat exchanger housingoutside of said conduit walls, including housing walls connected to saidconduit walls in a position to form a jacket chamber surrounding atleast a portion of said acoustic standing wave, said chamber containingand holding a fluid to be heated in heat transfer contact with theoutside surface of said conduit walls, and isolated from the gaseswithin said conduit, an inlet through which fluid to be heated may beadmitted to said chamber, and a heated fluid outlet conduit leading fromsaid chamber toward a point of utilization located externally of saidchamber, all in such manner that the acoustic standing wave in saidconduit dissipates the heat insulating boundary layer of stagnant gasesadjacent the inside surface of the walls thereof while heat is beinggenerated in the combustion gas body inside said walls and transferredthrough said walls to the fluid within said housing.

2. A jet engine type heater comprising: an acoustic cavity in the formof a U-shaped sonicpipe having walls defining a guide for a resonantstanding wave in a combustion gas body therein, combustion chambers atthe tion of the sonic pipe, and a housing enclosing substantially theentirety of said U-shaped sonic pipe including the velocity antinodesection thereof, said housing holding a fluid to be heated in heattransfer contact with the outside surface of said sonic pipe, wherebythe acoustic standing wave in the sonic pipe dissipates the heatinsulating boundary layer of stagnant gases adjacent the inside of saidsonic pipe while heat is being generated in the combustion gas bodyinside said pipe and transferred

